1. Field of the Invention
The present invention relates to a method and system for accessing a digitized microscope slide from a remote workstation, wherein a plurality of digitized microscope slides are stored in a plurality of data station units.
2. Background Art
The analysis of tissue sections is an important field of medical diagnostics. For conducting a tissue analysis the tissue specimen taken from a patient is sliced up in very fine sections (e.g. 2-10 μm thick sections), which are then placed on glass plates and are stained with various dyes. Finally, the slide bearing the resulting specimen is analyzed/examined with a microscope.
The efficiency of the analysis can be substantially enhanced by virtual slide imaging, where the specimen slides are first digitized and can be viewed and analyzed afterwards in a convenient manner by suitable software applications. Virtual slide imaging is becoming more and more widespread as it offers a higher degree of freedom compared to conventional live microscopy where microscope specimen slides are viewed in real time and are examined by a person viewing the slide. The digitized microscope slides allow for faster viewing (since the images are already captured), for annotation of the specimen regions of interest, for computerized analysis of the specimen (e.g. finding given type of cells, measuring their area, etc.) and for an unlimited number of reviewing for diagnostic or educational purposes.
Since the digitized microscope slides are stored in electronic files the possibility of transferring these files to and reviewing at a remote computer is at hand. However, the digitized microscope slides tend to be extremely large. The specimen slides are digitized by an imaging device, which generally comprises a camera coupled to a microscope. The field of view of the resulting optical system corresponds to a relatively small portion of the whole slide, therefore, in order to scan the whole slide, the slide is divided into fields corresponding to the field of view of the optical system and an image is captured of each field. The individual images called image tiles are then aligned (or “stitched” together as commonly referred to) in a software application to form a single continuous image of the specimen slide. For example, the useful (net) surface area of a slide can be 25 mm by 50 mm. Applying a commonly used resolution of 0.3 μm, this means approximately 83 000 by 166 000 pixels. If each pixel is represented on 3 bytes, as is the standard practice, at a compression rate of 1:10, the size of the resulting file would still be 3.8 GB. The digitized microscope slides are usually stored in a plurality of files, however this does not reduce the overall data amount that has to be transferred if the slide is to be examined on a remote computer.
A further aspect to be taken into account when creating a digitized microscope slide is to allow for conventional type of slide examination, which implies viewing the digitized microscope slide at different magnifications. In conventional live microscopy the examining pathologist first examines the specimen slide using a low magnification objective in order to gain an overall view of the specimen and possibly to locate regions of interest, which he then reviews using a higher magnification objective. Conventional microscopes can have three or even more different magnification objectives, it is therefore required to allow for reproducing at least these magnifications in virtual microscopy as well. This is usually done by down-scaling the images taken with a high-resolution, high-magnification objective. For example, in order to display an image captured using an objective of 20× magnification as if it were taken using an objective of 4× magnification, the image is to be reduced digitally at a rate of 5:1 in both directions x and y. However the image viewing application must still handle a file that is twenty-five times larger than the one actually needed, which can lead to unacceptable deceleration. The commonly used solution is to down-scale the images during or after the digitization and store the images at a plurality of different magnifications, thus a single digitized microscope slide generally comprises images of the specimen slide at a number of different magnifications.
The size and number of files can further increase in the case of fluorescent microscopy. Most image formats store a maximum of three color channels, however in the case of fluorescent microscopy a number of different fluorescent filters may be applied for viewing the same specimen slide at a number of different wavelengths resulting in further data amount.
Moreover, with the spreading of Internet there is an ever-growing demand for transferring or viewing digitized microscope slides over the Internet. A similar desire can arise in the case of computers connected by Intranet, or a local area network (LAN) for example in a hospital or a research institute where the specimen slides are being digitized by a computer controlled camera coupled to a microscope and are to be viewed and examined by a pathologist working with another computer. The commonly used solution is to store the digitized microscope slides in a central computer or server accessible by a number of remote workstations connected to the central computer by a communication network (Internet, Intranet, LAN or any other communication network), thus all or part of the images of a digitized microscope slide can be downloaded or viewed over the communication network.
U.S. Pat. Appl. No. 2006/0188137 discloses a method and an apparatus for viewing digitized microscope slide images including transmitting image tiles of the slide from a central server to a remote client. The client assembles the tiled images into a seamless virtual slide and provides tools for manipulating image magnification and viewpoint.
Making use of a single server for storing the digitized microscope slide can lead to very high bandwidth requirements, especially if a large number of clients are likely to request viewing or downloading of files simultaneously.
It would also be desirable to view digitized microscope slides located on not just one server but rather on a plurality of servers or computers, for example on servers run by different hospitals or research institutes or personal computers of doctors or members of a research team.